1. Field of the Invention
This invention relates to a head loading/unloading control method and storage device for moving away a head that reads a storage medium from the storage medium when it is not needed.
2. Description of the Related Art
Storage devices that have a head for reading storage medium are widely used. For example the magnetic disk drives used as a storage devices for computers comprise a magnetic disk, a head for reading from and writing to the magnetic disk, and a VCM actuator for positioning the head on a track of the magnetic disk. The storage density of these kinds of disk drives is rapidly increasing, and compact disk drives are currently being developed for them. Compact disk drives are separate and portable, and can also be used as the external storage device of a portable handheld computer.
Hard disk drives comprise a magnetic disk, a magnetic head, a VCM actuator, and a flexure (suspension). In this kind of hard disk drive, as the density of the magnetic disk has increased in recent years, the distance that the magnetic head floats above the magnetic disk has decreased. Therefore, the magnetic head can easily come in contact with the magnetic disk by even a small vibration and damage both the disk and head.
In order to prevent this, a hard disk drive has been proposed (for example in Japanese Unexamined published patent No. H6-60578) in which a ramp is installed at a position away from the magnetic disk, and when the head is not in operation, it moves to the position of the ramp so it is out of the way (this is called the unloading operation).
Recent hard disk drives and the electronic devices (computers, etc.) in which they are installed have become more and more portable. Therefore, the hard disk drive is used in an environment in which it is easy for it to receive external vibration. Moreover, since the electronic devices are driven by battery, the capacity of the power supply is limited. Therefore, it is desirable to reduce the power consumption.
To meet this demand, in prior storage devices, when there is no access (I/O command) for a continuous time, that time is counted, and when it reaches a specified time, the aforementioned unloading operation is performed and the head is moved away from the magnetic disk. In this method, when there is no access for a specified time, the head moves away from the magnetic disk, so it is possible to prevent damage to the disk and head even when there is external vibration. Also, since the ramp is supported mechanically, there is no need for drive current to flow to the VCM, so it is also possible to reduce the power consumption. Moreover, when there is access, the head returns from the ramp to the magnetic disk (this is called loading), and in this way the head is loaded only when in operation.
However, the prior art had the following problems.
(1) In the prior art, the specified time from when there was no more access until unloading started was fixed. This time is short (for example: 3 seconds) since there is a demand to keep the head unload for as long as possible when it is not in operation. Therefore, the unloading operation is performed frequently. In this unloading and loading operation, the ramp and the head slide against each other so there is the problem that the ramp is easily worn and had a short life. Normally, the ramp is made of a non-metallic material such as synthetic resin or plastic so that it is not abrasive to the metal material of the head, so it is worn by rubbing movement. The surface of the ramp is initially flat and smooth, and there is little dust that is generated by the sliding movement, however, as the surface is worn by the sliding motion, the surface becomes uneven, and relatively large particles begin to be worn away by the sliding motion. These large particles adhere to the disk and head causing data error to frequently occur. Therefore, it is necessary to set the life of the ramp to before this condition occurs. For example, approximately 300,000 times. When loading and unloading are frequently performed in order to improve the resistance to impact as described above, the ramp quickly reaches the end of its life. In compact storage devices such as a hard disk drive, the parts are very small, so replacement of just the ramp is almost impossible. Therefore, when the ramp reaches the end of its life, it is essentially the end of the life of the device itself. There is the problem of the life of the device being shortened by the ramp reaching the end of its life too quickly.
(2) Moreover, since the specified time is fixed, there is also the problem of decreased access time depending on the operating and access conditions.
(3) Furthermore, since the specified time is fixed, there is also the problem that it is not possible to effectively reduce the power consumption depending on the operating and access conditions.
The objective of this invention is to provide a head loading/unloading control method and a storage device for adequately performing the unloading operation in accordance to the state of the device.
Another objective of this invention is to provide a head loading/unloading control method and a storage device for lengthening the life of the device even when the unloading operation is performed.
Yet a further objective of this invention is to provide a head loading/unloading control method and a storage device for preventing a decrease in access time even when the unloading operation is performed.
Even yet a further objective of this invention is to provide a head loading/unloading control method and a storage device for further decreasing the power consumption even when the unloading operation is performed.
In order to accomplish these objectives, the head loading/unloading control method of this invention comprises: a step of unloading a head to a position away from a storage medium when the amount of time when there is no access command continues for a specified time; a step of loading the head to the storage medium when receive said access command; and a step of changing the specified time according to a status of a storage device.
In this form of the invention, the specified time that was formerly fixed (unload start time) is variable and is changed according to the state of the device. Therefore, it is possible to optimally perform the unloading operation according to the state of the device. In other words, an unloading operation becomes possible in which there is a balance among the device life, access time, and resistance to shock.
In another form of the invention, the step of changing the specified time comprises a step of counting the number of unloads, and a step of changing the specified time when the number of unloads exceeds a specified value. In this form of the invention, the specified time changes according to the number of unloads, so it is possible to increase the life of the device while at the same time maintain its resistance to shock even when the unloading operation is performed.
Other forms of the invention are as follows:
A step of changing the time comprises a step of changing the specified time according to the access state of the device. In this form of the invention, the specified time is changed according to the access state so it is possible to minimize the decrease in access time as well as decrease the power consumption even when the unloading operation is performed.
A step of changing the time comprises a step of changing the specified time according to the environment of the device. Since the specified time is changed according to the environment of the device, such as the installation location, temperature, frequency of shock, remaining battery charge, etc., it is possible to increase the effect of the invention such as improving the resistance to shock and decreasing the power consumption.
The storage device of this invention comprises a head that at least reads from a storage medium, an actuator for positioning the head, a ramp mechanism that support the head and which is installed at a position away from the storage medium, and a control means for unloading the head to the ramp position away from the storage medium when the amount of time that there is no access command reaches a specified time, and for loading the head to the storage medium when there is an access command, and where this control means changes the specified time according to the state of the device.
In this form of the invention, the specified time that was formerly fixed (unload start time) is variable and is changed according to the state of the device. Therefore, it is possible to optimally perform the unloading operation according to the state of the device. In other words, an unloading operation becomes possible in which there is a balance among the device life, access time, and resistance to shock.
The storage device of another feature of the invention comprises a head that at least reads from a storage medium, an actuator for positioning the head, a ramp mechanism that supports the head and which is installed at a position away from the storage medium, a control method for unloading the head to the ramp position away from the storage medium when the amount of time that there is no access command reaches a specified time, and a counter for counting the number times unloading is performed.